Acute compartment syndrome is a limb-threatening condition if not recognized and treated promptly. Appropriate management includes early fasciotomy, which often results in better functional outcomes. Although there are many causes of compartment syndrome, the common findings are significant pain, swelling, and limited range of motion. Diagnosis is usually based on physical findings in the setting of a compelling history. Before surgical intervention, the diagnosis is usually confirmed by measuring elevated compartment pressures. The patient described in this case report developed acute compartment syndrome of the forearm after his hand became trapped in machinery that applied sudden supination to the hand, and avulsed the distal portion of the left index finger. There was no direct trauma to the forearm. In this case, acute compartment syndrome was likely due to a combination of contained hemorrhage into the muscle sheath, closed muscle strain causing edema, and possibly axial traction applied to the tendons of the index finger. Acute compartment syndrome should be considered in the differential diagnosis for any patient complaining of severe pain in an extremity, even in the absence of commonly recognized mechanisms of injury.